The present disclosure relates generally to masking and, more particularly, to a method an apparatus to mask turbine components.
Gas turbine engines, such as those that power modern commercial and military aircraft, generally include a compressor section to pressurize an airflow, a combustor section to burn hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases.
The compressor and turbine include one or more arrays of blades extending radially outwardly from a rotatable rotor hub. Each blade has a root that mates with a slot in the rotor hub to retain the blade. Each blade also has a platform that partly defines a circumferential inner boundary of an engine flowpath, and an airfoil that extends radially across the flowpath. During engine operation, a working medium, which flows axially along the flowpath, receives energy from the compressor blade arrays and provides energy to the turbine blade arrays. Those portions of the blades that come in direct contact with the working medium are subjected to a demanding operational environment. This is particularly true of the turbine blades, which are exposed to the elevated temperature and damaging effects of combustion products discharged from the engine's combustion chamber.
Various protective coatings are applied to the flowpath exposed surfaces of the blades to extend their useful life. Application of such coatings to other portions of the blades may be undesirable, since the presence of a layer of coating can interfere with the installation of the blades into the hub. Accordingly, various fixtures facilitate the application of a protective coating to selected portions of a blade, while shielding non-selected portions of the blade from the application of the coating. These fixtures are normally used in conjunction with a coating application apparatus such as a low pressure plasma spray coater or a physical vapor deposition coater.
Existing fixtures lasts only a limited number of coating cycles. During each coating cycle, a quantity of the coating accumulates on the fixture itself. After a number of coating cycles, further use of the fixture results in the formation of a coating “bridge” between the fixture and the blade platform. Once this bridge is established, it may become difficult to remove the blade from the fixture without chipping the coating from the platform and rendering the blade unsuitable for service. The blade must then be stripped and recoated.
To avoid the potential chipped coating damage to the blades, each fixture is typically used only a limited number of times and then is temporarily removed from service and refurbished by stripping the accumulated coating from the fixture with an acidic solution. This maintenance is relatively time consuming and expensive. Moreover, because each fixture is serviceable for only a limited number of coating cycles, a relative significant inventory of fixtures must be available so that the supply of serviceable fixtures is sufficient to support uninterrupted production runs.